Electrostatic separation of dry materials



July 29, 1969 B. C. SCHMID ELECTROSTATIC SEPARATION OF DRY MATERIALS 2 Sheets-Sheet 1 Filed 25, 1967 INVENTOR Byron C. Sc/vnid II Ill/I,

ATTORNEY July 29, 1969 SCHM'D 3,458,040

ELECTROSTATIC SEPARATION OF DRY MATERIALS Filed Aug. 25. 1967 2 Sheets-Sheet 2 E LE CTR O 0 E INVENTOR 35/7072 C. .5 c 7277220 BY f3,

ATTORNEY United States Patent Int. Cl. B03c 7/06 US. Cl. 209-12 14 Claims ABSTRACT OF THE DISCLOSURE A rotatable, inclined, grounded cylinder of alternate longitudinal strips of conducting and non-conducting material and having internal nonmetallic ribs, is continuously supplied with material from the upper end thereof; the heavier, relatively denser, components of the material (e.g. metal) are fed toward the upper end of the cylinder by the helical ribs while the lighter material (e.g., dielectric material), having little mass, frictionally adheres to the cylinder and is rotated thereby almost to the high point and then drops into engagement with a relatively lower point along the cylinder. This process is repeated and the lighter material will be gradually fed to the lower or discharge end of the cylinder. Electrostatic means along the cylinder charges the particles of the lighter material and increases its frictional engagement with the cylinder so that it tends to rotate therewith toward a radially higher point before it drops back to the bottom of the cylinder, thus increasing the effectiveness of the separation of the lighter material from the heavier material.

Background of the invention The apparatus is useful in the art of separating dry materials, for example, waste wire materials in a factory may be chopped into relatively small pieces and subjected to the action of a hammermill to separate insulation from the Wire. It is desirable to completely separate the insulation from the metal wire so that the latter can be reclaimed. There are many other arts, for example, in the separation of tobacco stems from leaf material in which one of the materials to be separated is heavier than the other material. Tobacco stern pieces, for example, are more solid than the leaf pieces, and accordingly the present apparatus is effective in the separation of such material. The prior art mechanisms have been devised for the electrostatic separation of the materials and the present construction makes use of such phenomena, but utilizes it in connection with the difference in gravity between two materials to be separated such as those re ferred to.

Summary of the invention The apparatus comprises an elongated cylinder containing internal helical flanges from one end of the cylinder to the other. The inclination of the helices and the direction of rotation of the cylinder are such that any relatively dense material remaining in contact with the helices during rotation of the inclined cylinder will be conveyed to the upper end of the cylinder. Lighter (e.g., dielectric) materials, for example, wire insulation, usually will tend to adhere by friction to the inside of the cylinder so that the individual particles are rotated in a plane perpendicular to the axis of the cylinder. The frictional engagement of the material with the cylinder decreases as the material approaches the highest point in the cylinder during rotation thereof, whereupon the particles drop vertically or at an angle to the rotation of the plane where the particles started to rotate with the cylinder. Therefore, as each particle drops, it comes in contact with the cylin- 'ice der at a point somewhat spaced from the point at which it started to rotate with the cylinder in the plane referred to.

The lighter particles therefore gradually progress toward the lower or outlet end of the cylinder instead of being fed upwardly by the helices and gradually reach a discharge point at the lower end of the cylinder. The more solid particles with greater mass have lower frictional engagement with the cylinder and during rotation thereof are not lifted to a substantial extent with the cylinder as it rotates. These particles of greater mass, therefore, contact with the helices to be fed or conveyed thereby toward the upper end of the cylinder to be discharged through a suitable opening.

I have found that if the particles of lower mass are acted on by an electrostatic means, the particles are caused to be rotated with the cylinder up to approximately the top limit of the cylinder before dropping to the bottom thereof, and hence as these particles drop they engage the lower part of the cylinder at points further removed from the points at which they started to be elevated by rotation of the cylinder. Thus, the lighter particles progress more rapidly and efiiciently toward the discharge end of the cylinder. The particles of greater mass are not electrostatically attracted to the interior of the cylinder and accordingly are conveyed upwardly therealong by the helices. To prevent the electrostatic discharge from carrying the lighter particles over the top center of the cylinder, a grounded shield device acting as a condenser adjacent the cylinder alters the potential of the electrostatic charges near the top center of the cylinder so that the lighter materials drop vertically from substantially the highest point in the rotation of the cylinder.

Brief description of the drawing FIGURE 1 is -a side elevation of the apparatus;

FIGURE 2 is a section on line 2-2 of FIGURE 1; and

FIGURE 3 is a similar view on line 33 of FIG- URE 1.

Description of a preferred embodiment of the invention Referring to FIGURE 1, a supporting plate 10 is pivoted at one end as at 11 to a base plate 12, the other end of which is provided with spaced standards 13- having adjusting openings 14 arranged in an arc of a circle concentric to the axis of the pivot 11. The openings 14 are adapted to receive pins 15 to support the plate 10 at any desired angle to the horizontal.

Above the plate 10 is arranged an elongated cylinder 16 made up of alternate longitudinal pieces of conductive material 17 and insulating material 18. The cylinder contains therewithin a plurality of helices 19 made of nonmetallic material. Six of these ribs are shown in FIGURE 3 and the cylinder 16 is rotated in a manner to be described, so that the helices act as conveyors to any material in contact therewith toward the upper end of the cylinder 16.

Bearing standards 22 are mounted on the plate 10 and carry grooved rollers 23 (FIGURE 2) receiving annular ribs 24 carried by the cylinder 16 adjacent opposite ends. Thus the cylinder 16 is supported by the plate 10 for rotation on its axis.

Any suitable means may be employed for rotating the cylinder. For example, a variable speed motor 28 (FIG- URE 1) may be mounted on the plate 10 and provided with a driving pinion 29 meshing with a gear 30 surrounding the cylinder 16.

Casings 34 and 35 extend around the cylinder 16 at points substantially spaced from each other and the interior of these casings communicate with the interior of the cylinder through openings 36 and 37, respectively, these openings all being identical. The sides of the casings 34 and 35 extend downwardly vertically to the plate as shown in FIGURE 2, and the lower portions of such casings constitute receptacles for the two materials to be separated. The two casings 34 and 35 have gates and 41, respectively, which may be opened for the withdrawal of material from the casing, although it will be apparent that the members 40 and 41 may be slidable drawers in which the material may collect.

A standard 45 is mounted on the plate 10 and carries at its upper end a hopper 46 into which the mixture of the material is to be fed. This material is moved by a screw conveyor 47 through an outlet 48 and thence through pipe 49 terminating in the cylinder 16 substantially centrally of the length thereof. The shaft of the conveyor 47 carries a pulley 50 around which passes a belt 51 driven from the pulley 52 of the motor 53.

Both ends of the cylinder 16 are open for the movement of air therethrough, and to supply a current of air a fan 58 surrounds the outlet 48 and is driven through a belt 59 operated by a motor 60.

Referring to FIGURES 1 and 3, two radially spaced elongated electrodes 65 and 65a are supported at their ends by posts 66 and 66a respectively carried by the plate 10. The two electrodes 65 and 65a charged with high voltage current to induce electrostatic charges in the passing pieces of conducting material 17 of the cylinder, thus charging the lighter particles therein and causing them to adhere to the interior of the cylinder so that they tend to rotate therewith beyond what would occur through the normal frictional engagement of such particles with the cylinder. Grounded brushes 68 engage the cylinder 16 as shown in FIGURE 3 to permit transfer of electrons.

Extending substantially semicircularly around the cylinder 16, as shown in FIGURE 3, is an insulating member 70 backed up by a metallic shield 71 substantially coextensive with the insulating member 70. The shield 71 is grounded as at 72.

The apparatus is intended for use in the separation of dry solid materials encountered in a wide variety of industrial operations, such as mining and related operations requiring separation of minerals and ores, food processing requiring, for example, separation of hulls from seeds or beans, tobacco processing requiring the separation of stems from leaf materials, etc. The device also has been effectively used for separating waste wires from insulation, which separation usually has been accomplished by burning off the insulation with a consequent pollution of the atmosphere and loss of some of the metal by oxidation.

Assuming the apparatus is to be used for separating such dielectric material as insulation from waste wire, the wire is chopped into relatively small pieces and the insulation loosened therefrom by subjecting the pieces to the operation of a hammermill. The material thus treated is fed to the hopper 46 and flows through pipe 49 into the cylinder 16 to be discharged substantially centrally of the length thereof. The wire pieces, loosened from the insulation, tends to slide around the cylinder 16 as the latter is rotated and is thus gradually fed by the helices 19 upwardly along the cylinder 16 to be discharged through the openings 36 for collection from the casing 34.

The insulating material being of less mass tends to frictionally engage the cylinder 16 to rotate therewith instead of being moved by the helices 19. It will be noted in FIGURE 1 that any plane traverses to the cylinder 16 perpendicular to the axis thereof will have its point intersecting the high point of the cylinder arranged to the right of its lowest point intersecting the bottom of the cylinder. As the lighter material is carried upwardly around the cylinder by friction, the frictional engagement decreases as the material moves upwardly and at some point usually above the horizontal plane of the cylinder axis, such lighter material will drop vertically and thus will be arranged to the right of the point occupied when its upward movement by the cylinder from the lowest point thereof began. This successive lifting and dropping of the lighter materials cause it to progress gradually toward the right hand end of the cylinder to be discharged through the openings 37 into the bottom of the casing 35 to be periodically removed.

If the light material can be caused to adhere to the cylinder until near the top thereof, each dropping of the material by gravity vertically to the bottom of the cylinder will represent slightly greater progress toward the right than if friction alone is depended upon. The electrode induces a charge in conductive pieces or segments 17 which in turn causes a higher degree of adherence of the nonconductive material to the cylinder. The insulating material of shield 71 at the top of the cylinder serves to alter the potential of the adjacent piece or segment 17, reducing adherence of the nonconductive pieces of material in the cylinder. Thus the progress of the materials of lighter mass toward the discharge end of the cylinder is expedited. The heavy conducting particles of wire or other material are not electrostatically affected, hence will slide along the surface of the interior of the cylinder to be intercepted by the helices to be thus conveyed thereby to the discharge openings 36. While the two electrodes 65 and 65a have been shown as arranged externally of the cylinder 16, it will be apparent that they may be arranged internally of the cylinder 16 in their respective radial planes.

The separation of the materials is further rendered more efficient by the use of the fan 58. The cylinder 16 is open at both ends and during the operation of the apparatus the fan blows a current of air downwardly through the cylinder 16. This current of air does not have appreciable effect on the heavier particles. However, as the lighter particles drop from the upper portions of the cylyinder, the current of air causes these particles to take a downward course to the right in FIGURE 1. Whereas, without the fan, the particles drop vertically as described above, the fan causes the lighter particles at each dropping thereof from the top portions of the cylinder to strike the bottom of the cylinder at a closer point toward the outlet end.

The inclination of the cylinder from the horizontal and the speed of rotation thereof readily may be determined by experimentation. For example, rubber insulated aluminum wire, chopped in pieces and fed to a hammermill as described may be supplied to the hopper 46 with the cylinder arranged at an angle of 11.5 from the horizontal and rotating at a speed of 50 r.p.m. The angle of the cylinder to the horizontal may be adjusted by inserting pins 15 in the openings 14, and the rheostat controlling the variable speed motor 28 may be adjusted to determine the speed of rotation of the cylinder.

From the foregoing it will now be seen that there is herein provided an improved apparatus for the electrostatic separation of dry materials which accomplishes all of the objects of this invention and others, including many advantages of great practical utility and commercial importance.

As various embodiments may be made of this inventive concept, and as many modifications may be made in the embodiments hereinbefore shown and described, it is to be understood that all matter herein is to be interpreted merely as illustrative, and not in a limiting sense.

I claim:

1. A separator for dry materials comprising a rotatable cylinder inclined from the horizontal, said cylinder comprising alternate longitudinal strips of conducting and nonconducting material, means for feeding material to be separated to the cylinder, nonmetallic means in said cylinder for moving heavier particles toward the higher end of said cylinder to be discharged therefrom, lighter dielectric particles adhering to the interior of the cylinder by friction to partake of a partial rotation perpendicular to the axis of said cylinder and then to drop vertically to thus progress toward the lower end of the cylinder to be discharged therefrom, electrostatic means for increasing the adherence of said lighter dielectric particles to the interior of the cylinder to be rotated approximately a half revolution of said cylinder, grounded means engaging the cylinder strips and means for rendering the electrostatic charging of said particles ineffective for causing the particles to adhere to the downwardly moving side of said cylinder whereby said particles will drop downwardly from substantially the highest point in said cylinder.

2. Apparatus according to claim 1 wherein said means for moving heavy particles towards the higher end of said cylinder comprises an internal helical rib within said cylinder, said cylinder being revolved with relation to the pitch of said helix so that said helix will engage the heavy particles to feed them toward said higher end of said cylinder.

3. Apparatus according to claim 1 provided with casings surrounding said cylinder adjacent opposite ends thereof, said cylinder being provided with openings for discharging heavier and lighter materials respectively into the casings adjacent the higher and lower ends of said cylinder.

4. Apparatus according to claim 1 wherein said means for moving heavy particles towards the higher end of said cylinder comprises an internal helical rib within said cylinder, said cylinder being revolved with relation to the pitch of said helix so that said helix will engage the heavy particles to feed them toward said higher end of said cylinder, and casings surrounding said cylinder adjacent opposite ends thereof, said cylinder being provided with openings for discharging heavier and lighter materials respectively into the casings adjacent the higher and lower ends of said cylinder.

5. Apparatus according to claim 1 wherein said cylinder is open at both ends, and means for forcing a current of air through said cylinder from the higher to the lower end thereof to expedite movement of the lighter particles towards said lower end of said cylinder.

6. Apparatus according to claim 1 provided with a plate on which said cylinder is rotatably supported, means for adjusting the inclination of said plate to the horizontal and hence the corresponding inclination of said cylinder, and a variable speed motor for rotating said cylinder.

7. Apparatus according to claim 6 provided with hearing standards carried by said plate adjacent opposite ends thereof, a pair of grooved wheels carried by each standard, an annular flange carried by said cylinder adjacent each end and each engaging the adjacent grooved rollers to be supported thereby for rotation, said cylinder being open at both ends, and means for effecting a flow of air through said cylinder from the higher to the lower end thereof to expedite movement of the lighter particles in said cylinder toward the lower end thereof.

8. Apparatus according to claim 6 provided with material receiving casings supported by said plate adjacent opposite ends of said cylinder, each casing having a portion extending upwardly, over and around said cylinder, said cylinder being provided with at least one opening communicating with each of said casings to discharge separated material thereinto.

9. Apparatus according to claim 1 wherein said electrostatic means comprises at least one elongated high voltage electrode arranged adjacent and parallel to said cylinder.

10. Apparatus according to claim 1 wherein said electrostatic means comprises an elongated high voltage electrode arranged adjacent and parallel to said cylinder.

11. Apparatus according to claim 10 wherein said cylinder is open at both ends, and means for effecting a flow of air through said cylinder from the higher to the lower end thereof whereby lighter particles dropping from the upper part of said cylinder to the lower part thereof will be moved longitudinally toward the lower end of said cylinder by said flow of air.

12. Apparatus according to claim 11 provided with a pipe arranged coaxially in said cylinder and projecting from the higher end thereof to a point intermediate the length of said cylinder, and means for feeding material to the higher end of said pipe to be discharged from the lower end thereof into said cylinder.

13. Apparatus according to claim 12 wherein said means for supplying material to be separated to said higher end of said pipe comprises a hopper with which such end of said pipe communicates, and a conveyor in said hopper for moving material therefrom into said pipe.

14. Apparatus constructed in accordance with claim 13 provided with a fan supported by said pipe coaxially thereof at the higher end of said cylinder for efiecting a flow of air through said cylinder.

References Cited UNITED STATES PATENTS 234,798 11/1880 Napier 209152 664,903 1/ 1901 Seldner 34-136 993,593 5/1911 Guernsey 209-473 1,043,349 11/ 1912 Ostwald. 1,744,967 1/1930 Johnson 209131 2,577,488 12/ 1951 Stephenson 209152 3,087,616 4/ 1963 Pierson 209221 FOREIGN PATENTS 16,287 1910 Great Britain. 57,185 1936 Norway.

FRANK W. LUTTER, Primary Examiner U.S. Cl. X.R. 

